[P-EM37_30PM1] 磁気圏構造とダイナミクス

[PEM37-12] THEMIS観測とMHDシミュレーションを用いた近地球プラズマシートにおけるプラズマ圧力の急激な増加に関する研究

*YAO YAO¹、海老原 祐輔¹、田中 高史² (1.京都大学生存圏研究所、2.九州大学宙空環境研究センター)

キーワード：サブストーム, THEMIS衛星観測, グローバルMHDシミュレーション, プラズマ圧力の急激な増加

Plasma pressure enhancement is one of the drastic substorm-associated phenomena in the inner magnetosphere. In a substorm occurred on 1 March 2008, four of THEMIS (Time History of Events and Macroscale Interactions during Substorms) probes were almost aligned along the sun-Earth line, which was suitable for investigating spatial-temporal evolution of the near-Earth plasma sheet in a substorm. They observed a sudden increase in the plasma pressure at the inner probe (at 〜7.2 Re), followed by the outer probes (at 〜7.5, 〜8.3, and 〜10.4 Re), that is the high pressure region propagates tailward. Hereinafter, we call this sudden pressure enhancement (SPE). We compared the observations with simulation results of a global magnetohydrodynamics (MHD) simulation, and found a fairly good agreement between them in terms of the followings. (1) Tailward propagation of the SPE can be seen only at off-equator after the substorm onset. In the equatorial plane, an earthward propagation of the SPE precedes the tailward propagation. (2) Observations from the three inner probes show that the SPE consists of two enhancements. The first one is attributed to the convergence of bulk flow energy flux, namely flow braking. The latter one is due to the convergence of the thermal energy flux and subsequent inflation of the plasma sheet. (3) Plasma flow turned from the tailward-and-toward-the-equatorial-plane to earthward-and-away-from-the-equatorial plane near the onset from the simulation results. We discuss the spatial-temporal evolution of the plasma flow and the magnetic field during the substorm.